1. Technical Field
The present invention relates to reagents for use in enzyme immunoassay (EIA) procedures.
2. Background Art
In immunoassay procedures typically used in clinical diagnostics, antibodies and antigens are conjugated with enzymes, forming enzyme conjugates, to detect the presence and/or amount of various analytes, i.e., antigens or antibodies in test samples prepared from biological fluids such as plasma, serum, spinal fluid or amniotic fluid. The presence and/or the amount of the analyte can be determined by measuring the formation of resulting antibody-antigen-enzyme complexes. The conjugated enzymes can, for example, activate suitable indicator substances, such as dyes which produce a colorimetric change resulting from interaction of the enzyme and the dye. The colorimetric change can be determined instrumentally by measuring the absorbance of the dye solution, or in some cases, visually, to provide an indication of the analyte. In addition to the use of enzyme conjugated antibodies to detect antigens, such EIAs can also be used to detect the presence of antibodies by reversing the roles of antigens and antibodies in the foregoing procedure.
Two major problems confronting the development of EIAs are sensitivity and reagent stability. Enzyme conjugate compositions used in such assays are usually prepared well in advance of the time the assay procedure is performed. Unfortunately, conventional conjugate compositions used as reagents in EIAs often suffer from substantial instability of their enzyme conjugates which causes their activity to diminish rapidly over time. This instability can be a significant disadvantage because shipping, distribution to customers and storage in inventory usually involve substantial time delays between conjugate preparation and use, and can also subject the preparations to wide temperature variations and other conditions which exacerbate activity degradation. Although current practices entail storage of enzyme conjugates in solutions such as saline and phosphate buffered saline, such solutions, used alone, have been found to provide inadequate stability when solubilized conjugates are subjected to temperature stress or stored for extended lengths of time. Accordingly, an enzyme conjugate composition which exhibits substantially improved stability characteristics by comparison with known compositions would be greatly advantageous.